Biology (from Greek: βίος, bio, "life"; and λόγος, logos, "speech") is the branch of science that studies life, including the origin, distribution, structure, and function of living organisms, as well as their classification. Biology evolved out of other natural sciences and medicine as a discipline of its own in the mid- to late-19th century. Along with chemistry and physics it is now one of the three sciences that are commonly taught in schools.

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Biological research underpins most of modern medicine. In turn, parts of biology are based off of chemistry. The knowledge of how enzymes and cells work is essential for the production of effective drugs. Biologists also study bacteria and viruses which cause illness and most importantly, can track what can and cannot kill them.

Biology also underpins evolutionary theory. Genetics and the study of DNA fall under biology as well as the tracking of evolutionary changes in species. Evolution is an important underlying principle of modern biology and is the basis for knowing where biological processes came from and how they will react to different stimuli.

Botany is the science of plants, and as such a subdiscipline of biology.

Plants have always been of prime importance to humans, primarily as food, but also as pasture for livestock, building material, fuel and herbal medicines (especially when nothing else was available). It is therefore not surprising that humans have accumulated vast amounts of relevant knowledge even before beginning to study them consciously and systematically. As an example, the ancient Babylonians already knew the benefits of hand pollination of date palms, long before plant sexuality was actually understood.

Major steps of progress in scholarly and protoscientific work on plants in Western civilization include the botanical writings of Theophrastus, Aristotle and Dioscorides in antiquity, followed by medieval herbals composed as lists of useful plants. The modern science of botany began to develop out of medicine and pharmacology; in fact, many old European botanical gardens started as herb gardens of medical professors. In 1753, Carl Linnaeus introduced the binary names that characterize modern taxonomy with his book Species Plantarum. A considerable but often neglected breakthrough was the explanation of animal pollination in plants by Christian K. Sprengel published in 1793. The 19th century saw a rapid increase in the number of known plant species as more and more excursions into tropical countries or colonies were undertaken. Many species could for the first time be cultivated and studied in greenhouses of temperate Europe and North America thanks to the invention of containers that allowed them to survive transport. Gregor Mendel, one of the fathers of genetics, at the same time conducted his influential research on selected species of plants, especially peas.

In the last few decades, molecular and laboratory methods have become increasingly important in botany. Evolutionary biology and systematics of plants rely increasingly on molecular data to reconstruct phylogenies and resolve the relationships between species. Intensive research has been conducted on a few model species to get a better understanding of genetic and developmental processes in plants, especially on Arabidopsis thaliana, a cabbage relative comparable in its scientific importance to the zoologist's fruit fly Drosophila melanogaster. Other recent additions to the research interests of botanists are biotechnology, the study of invasive organisms and the impact of global change on plant communities.

Physiology is the study of the processes that occur within all living organisms. Many of these processes are directly or indirectly homeostatic, and include the interactions between cells, tissues and organs as well as all intracellular communication.

Zoology (from Greek ζῷον, zoon, "animal" + λόγος, logos, "knowledge") is a subfield of biology that focuses on the form, behaviour and evolution of animals such as the goat or long-eared jerboa. As a very broad discipline, zoology itself has many subfields, such as herpetology, which focuses on amphibians and lizards. Although it has roots in ancient China and the Arab world (before it went nuts) most modern zoology was started in the 19th century, when the Victorian obsession for knowledge and the invention of new technologies caused hundreds and thousands of naturalists to document the animal kingdom in unprecedented detail. The advances in science brought about by zoology during this period, particularly in documenting the similarities behind groups of animals, led to the development of the theory of evolution by natural selection in 1859 by Charles Darwin.

Biophysics is an interdisciplinary branch of biology, chemistry and physics. Basically this branch of science uses physics to study all levels of biology.

Biophysics is a wellspring of innovation for our high-tech economy. The applications of biophysics depend on society’s needs. In the 20th century, great progress was made in treating disease. Biophysics helped create powerful vaccines against infectious diseases.[4] It described and controlled diseases of metabolism, such as diabetes. And biophysics provided both the tools and the understanding for treating cancer. Biophysical methods are increasingly used to serve everyday needs, from forensic science to bioremediation.